Field of the Invention
The present invention relates to anticaking and anticorrosion agents for inorganic salts.
Description of Related Art
When exposed to conditions of varying atmospheric humidity, inorganic salts, such as sodium chloride (NaCl), cake or harden due to the formation of crystalline salt bridges that effectively welds adjacent salt crystals together. This results in the formation of large clumps, as well as a hardened crust on the surface of salt piles, and is detrimental to the ease of handling and applying the salt. This agglomeration, clumping, crusting, and/or hardening between individual salt granules is referred to herein (and in the art) as “caking.” Caking occurs because of the hygroscopic nature of salt. Thus, at higher humidity, water is trapped between adjacent salt granules and dissolves salt at the crystal interface. This water evaporates as the humidity falls, which leaves behind a salt bridge or weld between and among the granules. Sodium ferrocyanide, also known as yellow prussiate of soda or YPS, has become well known as an effective anticaking agent for sodium chloride. However, YPS is undesirable in certain applications, such as those that involve the electrolytic generation of chlorine (e.g., industrial chloralkali processes and/or salt water pool chlorinators). These processes use electricity to convert chloride anions (Cl−) into free available chlorine (Cl+) in the form of sodium hypochlorite (NaOCl). During the electrolytic process, chlorine can react with nitrogen-containing compounds such as ammonia or the cyanide moiety of YPS to produce volatile, explosive nitrogen trichloride (NCl3). In order to minimize the formation of undesirable NCl3, operators limit or proscribe the use of nitrogenous compounds for the electrolytic generation of chlorine. Moreover, YPS is the subject of continuing environmental scrutiny, which underscores the need for YPS-free and nitrogen-free anticaking agents for inorganic salts.
In light of YPS's undesirability for certain applications, alternative compositions and methods to deter the caking of inorganic salts have been developed, including the use of carbohydrate-metal complexes, iron ammonium complexes of polyhydroxycarboxylic acids, tartaric acid, and meso-tartaric acid. However, these alternatives have several drawbacks. For example, meso-tartaric acid is very expensive to purchase and difficult to prepare. Meso-tartaric acid requires heating a solution of d-tartaric acid in sodium hydroxide for two hours at 118° C. (244.4° F.). After cooling this solution, hydrochloric acid must be added to adjust the pH to 6.
In addition to caking and hardening, another consideration when using inorganic salts is the corrosion they can cause when used to device roadways. In view of these concerns, organizations such as the Pacific Northwest Snowfighters (PNS) Association have set specifications for products used to melt snow and ice. This consortium of U.S. and British Columbia transportation agencies mandates tests to measure the corrosion rates in deicers in accordance with the National Association of Corrosion Engineers (NACE) Standard TM0169, as modified by PNS. In order for a corrosion inhibited snow and ice control product to meet this standard, it must demonstrate that it is at least 70% less corrosive than sodium chloride alone. Improved compositions and methods that can prevent or reduce the caking of inorganic salts and concomitantly reduce corrosion would be exceptionally useful and novel.
In addition to anticaking agents for bulk deicing salt, various substances are used with edible salts, such as potassium or sodium chloride. For example, silicon dioxide has been used in food salt as an anticaking agent. Garlic, onion, peppers, herbs, spices, and sugars are often mixed with salts to reduce caking as well as impart unique flavors to food grade salts. Various acids, such as uric acid, lactic acid, citric acid, and malic acid can act as taste modifiers for edible salts. The use of acids, such as malic acid, for taste modification however, requires the acids to be applied in the acid form in order for them to impart the desired flavor. That is to say, neutralization of the acidulants renders them non-acidic and destroys their ability to produce the desired tanginess.
Thus, there remains a need in the art for improved anticaking agents for inorganic salts, such as NaCl, KCl, and MgCl2.